This invention relates to wind power energy and, more particularly, to a wind power energy system that produces a generally constant pressurized air pressure with modest heat energy loss to generate reliable electrical output.
Wind power is a rapidly growing segment of the electric power generation industry. A “dedicated generator” design utilizes a wind turbine to input rotational energy directly into an electric generator to generate and supply electricity to a power grid. The wind turbine is connected to a gearbox that converts the typical fifteen to thirty revolutions per minute of the wind turbine to 1500 to 3600 revolutions per minute required for an electric generator. The gearbox is a noisy, heavy, and expensive component of the wind tower and it is generally desirable to eliminate it from the wind tower design.
Another type of wind tower design utilizes a wind turbine to drive a compressor that produces pressurized air, which is stored in a tank. Pressurized air rotates a turbine attached to an electric generator to supply electricity to the power grid.
In particular, several drawbacks exist for conventional wind power systems with regard to electricity generation. For one, the amount of energy produced by conventional wind towers varies. One contributing factor to the variation is natural variation in wind speed. For the dedicated generator design, wind speed variation leads directly to spikes in the amount of electricity that the generator produces. For pressurized air storage designs, wind speed variation leads to variation in the pressure of the stored pressurized air. More importantly, in conventional designs the varying amount of electricity supplied to the power grid makes wind generated power difficult to sell in the energy market, which requires selling power more than twenty-four hours in advance.
Some conventional wind power systems utilize supplemental power input. When the amount of electricity generated by a conventional wind power system fails to meet the required demand, additional electricity from a remote off-site generator is transmitted to the wind power site to supplement the wind power electricity. This introduces significant additional costs, infrastructure, and inefficiencies to the system.
Other conventional wind power systems utilize two types of wind towers. One tower generates electricity for immediate use and another type of tower produces pressurized air to store energy for later generation of electricity. When wind conditions are inadequate for the first type of tower to immediately meet electricity demands, the pressurized air produced by the second type of tower can be utilized to generate supplemental electricity. Although this type of wind power system addresses variation in electricity generation, there is still demand for more efficient wind power systems.
In the power industry in general, a dual input generator utilizes the input of a first combustion engine to generate electricity and the input of a second combustion engine to supplement the first combustion engine when additional electrical output is desired. Combustion engines, however, utilize conventional hydrocarbon fuels and therefore suffer considerable expense and environmental impact.
Another drawback for conventional pressurized air wind power systems is inadequate operational efficiency. The percent of wind energy that actually results in electric energy produced is typically less than forty percent for conventional wind towers. The considerable loss in efficiency can come from a variety of sources. For one, the loss of heat energy when air is compressed accounts for approximately fifty percent of the total energy lost. The compression ratio produces pressurized air having an extremely high temperature, for example 600° C. The extreme temperature and heat exceeds a maximum temperature limit of the materials making the wind power system and must therefore be dissipated in order to avoid failure of the system. Dissipation occurs through intercooling in the compression system and loss of heat to the outer surrounding environment.
Another source of operational efficiency loss in conventional pressurized air wind power systems is waste of potential power from turbine rotation when the wind speed varies from a pre-selected design point. The rotational speed of the wind turbine scales linearly with wind speed, but the power generated by the wind turbine scales with the cube of the wind speed. This forces either the air compressor compression ratio to vary strongly with wind speed or the wind turbine to operate far away from peak aerodynamic efficiency in order to dissipate or forego a portion of wind power. The resulting inefficiencies lead to higher expense to produce wind generated electricity.
Despite dual input generators and existing conventional wind power systems, a demand remains for a wind power system that is reliable, efficient, and cost effective. Accordingly, it is desirable to provide a wind power system with low variation in the amount of electricity generated and high operational efficiency.